1. Field of the Invention
The present invention relates to an alignment method to align one image frame with another image frame, and an alignment system that aligns one image frame with another image frame. In particular, the alignment method of the present invention can automatically align image frames in recorded video clips, and the alignment system includes a machine readable storage medium that provides instructions that cause the machine to perform operations to align image frames.
2. Description of the Related Art
Recently, infrared (IR) video cameras have been investigated for volatile organic compounds (VOC) leak detection as a cost-effective alternative. The approach of using IR cameras for leak detection is often referred to as a smart leak detection and repair (LDAR). These cameras are operated at a predetermined wavelength band with strong VOC absorptions. All background objects emit or reflect IR rays with various intensity at the camera's wavelength band, causing formation of a background image on the detector array of the camera. When VOC is emitted from a leaking component, the VOC vapor forms a plume in the atmosphere. If the VOC plume is in between the background and the camera, the VOC will absorb the IR rays emitted or reflected by the background objects. The absorption will make the plume appear as “smoke” in front of background in the image captured by the IR camera. The intensities of the plume image pixels depend on the gas concentration and camera sensitivity. This kind of cameras can be operated manually by operators to scan possible leaking components. Usually, several seconds of video length are enough for an operator to identify the leaking gas plume within an area covered by the viewfinder of the camera. The camera can also be mounted at a fixed location to continuously monitor a large operational area within a refinery or a chemical plant. The fugitive VOC emissions due to leak in equipment can be reduced if the leaking equipment can be found easily and repaired promptly, because the duration of leaking is minimized.
To improve accuracy and to further reduce labor cost, it is desirable to process the IR video automatically. The IR video data processing includes automatic identification of VOC plume in a non-attendant manner, quantification of the relationship between the image and the actual VOC leaking rate, and compression of the video images to save data storage space.
In order to accomplish some of these automated tasks, frames in the IR video need to be closely aligned to the same frame of reference. A video footage consists of many frames. These frames in a raw video footage are usually not in the same reference spatially as the camera shift positions during recording. When the camera experience moving, shaking, or vibration, a frame may capture a slightly different scene compared to its immediate preceding frame, or the captured scene may be rotated. The unstable camera may be caused by the operator, process equipment, or strong wind if it is mounted on a tall structure. For practical industrial applications, this vibration becomes inevitable and the unaligned frames will make those image processing algorithms fail. Therefore, the video frames have to be aligned before a quantitative processing can be performed.
To transform an image to match another image is called image registration. The alignment of the video frames includes a series of image registration process. At present, all image processing software packages use manually selected control points for image registration, and only provide local registration.
Therefore, in order to solve the problems mentioned above, the present invention provides a method for automatically aligning images frames and an alignment system that automatically aligns image frame.